1. Field of the Invention
The invention relates to a spread spectrum secondary channel which occupies the same bandwidth as a primary data channel in a system wherein modems are transmitting and receiving information on a communications medium such as a telephone line.
2. Description of the Prior Art
Secondary channels have been used in high-speed (greater than or equal to 2400 bits per second) wireline modems to provide low speed (110 bits per second) non-interfering communications for control or monitoring functions. For instance, a secondary channel has been used in modems manufactured by the Paradyne Corporation (the assignee of the present invention) in their "Analysis" system. The "Analysis" system allows the user to monitor, configure, and test the modems in the network using commands sent over the secondary channel. Secondary channels are also used in low-duty cycle applications such as with alarms or teletype data transmission.
Secondary channels have also been implemented by using a completely independent Frequency Shift Keyed (FSK) channel that is placed in an unused portion of the telephone line spectrum.